The obvious play is to cast it during your opponent's upkeep to skip their turn, in which case it is a Time Stretch with the downside of letting them untap once. However, the fact that it can be used for shenanigans involving skipping delayed triggers and the like gives it its own niche.

(Speaking of which, did anybody else ever think that Jace, the Mind Sculptor looks like he's casting Time Stretch?)

As an aside, this card exiles itself from the game before it finishes resolving (when the turn ends, all cards on the stack are exiled, including Theft of Time.) Like Time Stop it would probably get reminder text, but it could easily support it.

For that reason, I would think that Time Stretch is more powerful, since it can be returned. But Time Stop costs more than Time Warp. Go figure.

All extra-turn cards exile themselves nowadays, though, specifically to prevent that sort of thing. If ending the turn didn't automatically exile it, I would have just had to write out "Exile Theft of Time" at the end anyway. This construction hides it in reminder text and makes it a little cleaner. (Maybe I should actually write out the reminder text...)

I thought it was neat that the exile clause was hidden inside the end the turn clause.

Seeing that both Timestop and Sundial of the Infinite have reminder text, I assume if this card was printed it would include reminder text. After all, it's a very rare card that includes the words, and it does some rather non-standard stuff. I wouldn't expect someone who's only played the game for one year to know what to do.

True enough. I never intended to imply it would be printed without reminder text. It's just long reminder text and I was being lazy :)